In 1221, he was married to Eleanor, daughter of Alfonso VIII of Castile. The next six years of his reign were full of rebellions on the part of the nobles. By the Peace of Alcalá of 31 March 1227, the nobles and the king came to terms.[5]

In 1228, James faced the sternest opposition yet from a vassal. Guerau IV de Cabrera occupied the County of Urgell in opposition to Aurembiax, the heiress of Ermengol VIII, who had died without sons in 1208. Although Aurembiax's mother, Elvira, had made herself a protegée of James's father, upon her death in 1220 Guerau occupied the county and displaced Aurembiax, claiming that a woman could not inherit.

James intervened on behalf of Aurembiax, to whom he owed protection. He bought Guerau off and allowed Aurembiax to reclaim her territory, which she did at Lleida, probably also becoming one of James' earliest mistresses.[6] She surrendered Lleida to James and agreed to hold Urgell in fief for him. On her death in 1231, James exchanged the Balearic Islands for Urgell with her widower, Peter of Portugal.

From 1230 to 1232, James negotiated with Sancho VII of Navarre, who desired his help against his nephew and closest living male relative, Theobald IV of Champagne. James and Sancho negotiated a treaty whereby James would inherit Navarre on the old Sancho's death, but when this occurred in 1234, the Navarrese nobles elevated Theobald to the throne instead, and James disputed it. Pope Gregory IX was required to intervene.[7] In the end, James accepted Theobald's succession.

James endeavoured to form a state straddling the Pyrenees in order to counterbalance the power of France north of the Loire. As with the much earlier Visigothic attempt, this policy was victim to physical, cultural, and political obstacles. As in the case of Navarre, he declined to launch into perilous adventures. By the Treaty of Corbeil, signed in May 1258, he ended his conflict with Louis IX of France, securing the renunciation of French claims to sovereignty over Catalonia. [3]

The Moors request permission from James I, taken from The Cantigas de Santa María

First compilation of the Fueros of Aragon, carried out by the bishop of Huesca Vidal de Canellas in 1247. Vidal Mayor.

After his false start at uniting Aragon with the Kingdom of Navarre through a scheme of mutual adoption, James turned to the south and the Balearic Islands in the Mediterranean Sea. On 5 September 1229, the troops from Aragon, consisting of 155 ships, 1,500 horsemen and 15,000 soldiers, set sail from Tarragona, Salou, and Cambrils[8] to conquer Majorca from Abú Yahya, the semi-independent Almohad governor of the island. Although a group of Aragonese knights took part in the campaign because of their obligations to the king, the conquest of Majorca was mainly a Catalan undertaking, and Catalans would later make up the majority of Majorca's settlers. James conquered Majorca on 31 December 1229, and Menorca (1232) and Ibiza (1235) were later acquired during the reconquest.

During his remaining two decades after Corbeil, James warred with the Moors in Murcia, on behalf of his son-in-law Alfonso X of Castile. On 26 March 1244, the two monarchs signed the Treaty of Almizra to establish their zones of expansion into Andalusia so as to prevent squabbling between them. Specifically, it defined the borders of the newly created Kingdom of Valencia. James signed it on that date, but Alfonso did not affirm it until much later. According to the treaty, all lands south of a line from Biar to Villajoyosa through Busot were reserved for Castile.

Abaqa, the "Khan of Tartary" (actually the Ilkhan), corresponded with James in early 1267, inviting him to join forces with the Mongols and go on crusade.[9] James sent an ambassador to Abaqa in the person of Jayme Alaric de Perpignan, who returned with a Mongol embassy in 1269.[10]Pope Clement IV tried to dissuade James from crusading, regarding his moral character as sub-par, and Alfonso X did the same. Nonetheless, James, who was then campaigning in Murcia, made peace with Muhammad I, the Sultan of Granada, and set about collecting funds for a crusade. After organising the government for his absence and assembling a fleet at Barcelona in September 1269, he was ready to sail east. The troubadour Olivier lo Templier composed a song praising the voyage and hoping for its success. A storm, however, drove him off course, and he landed at Aigues-Mortes. According to the continuator of William of Tyre, he returned via Montpellier por l'amor de sa dame Berenguiere ("for the love of his lady Berengaria") and abandoned any further effort at a crusade.

James's sons Pedro Fernández and Fernán Sánchez, who had been given command of part of the fleet, did continue on their way to Acre, where they arrived in December. They found that Baibars, the Mameluke Sultan of Egypt, had broken his truce with the Kingdom of Jerusalem and was making a demonstration of his military power in front of Acre. During the demonstration, Egyptian troops hidden in the bushes ambushed a returning Frankish force that had been in Galilee. James's sons, initially eager for a fight, changed their minds after this spectacle and returned home via Sicily, where Fernán Sánchez was knighted by Charles of Anjou.

James was the first great sponsor and patron of vernacular Catalan literature. Indeed, he may himself be called "the first of the Catalan prose writers."[11] James wrote or dictated at various stages a chronicle of his own life in Catalan, Llibre dels fets, the first autobiography by a Christian king. As well as being a fine example of autobiography, the "Book of Deeds" expresses concepts of the power and purpose of monarchy, examples of loyalty and treachery in the feudal order, and medieval military tactics. More controversially, some historians have looked at these writings as a source of Catalan identity, separate from that of Occitania and Rome.

Though James was himself a prose writer and sponsored mostly prose works, he had an appreciation of verse.[12] In consequence of the Albigensian Crusade, many troubadours were forced to flee southern France and many found refuge in Aragon. Notwithstanding his early patronage of poetry, by the influence of his confessor Ramon de Penyafort, James brought the Inquisition into his realm in 1233 to prevent any vernacular translation of the Bible.[12]

The favour James showed his illegitimate offspring led to protest from the nobles, and to conflicts between his legitimate and illegitimate sons. When one of the latter, Fernán Sánchez, who had behaved with gross ingratitude and treason toward his father, was slain by the legitimate son Peter, the old king recorded his grim satisfaction.

In his will, James divided his states between his sons by Yolanda of Hungary: the aforementioned Peter received the Hispanic possessions on the mainland and James received the Kingdom of Majorca, which included the Balearic Islands, the counties of Roussillon and Cerdanya, and the Lordship of Montpellier. The division inevitably produced fratricidal conflicts. In 1276, the king fell very ill at Alzira and resigned his crown, intending to retire to the monastery of Poblet, but he died at Valencia on 27 July.

His mummified body was later exhumed in 1856, when the monastery was under repair. A photograph of the king was taken. The photograph of the head of the mummy clearly shows the wound in the left eyebrow that the king himself explained in a passage from his Llibre dels fets (Book of Deeds):

As I was coming with the men, I happened to turn my head towards the town in order to look at the Saracens, who had come out in great force, when a cross-bowman shot at me, and hit me beside the sun-hood, and the shot struck me on the head, the bolt lighting near the forehead. It was God's will it did not pass through the head, but the point of the arrow went half through it. In anger I struck the arrow so with my hand that I broke it: the blood came out down my face; I wiped it off with a mantle of "sendal" I had, and went away laughing, that the army might not take alarm.[13]

^Herradón, Oscar (2008). Jaime I el Conquistador, el rey cruzado (James I the Conqueror, king of the crusades). Historia de Iberia Vieja: revista de historia de España (History of Ancient Iberia: review of the history of Spain). p. 15. ISSN1699-7913.